Within the field of windmills, it is commonly known that in order for a windmill to generate an optimal yield, the aerodynamic conditions of the windmill, including especially the aerodynamic conditions of the rotor blade, must be met. Thus, the manufacturers of windmills place great effort into making the rotor blades as efficient as possible in order to generate a good operating ratio. This does not only include the shape of the rotor blades, but also the surface character of the rotor blade, as it is an object to manufacture a surface which is as smooth as possible.
However, it is also realized that after a somewhat brief period of operation, e.g. six months, the rotor blades of a windmill may be so dirty from dust, salt coatings, dead insects, bird droppings and other surface coatings, that the efficiency of a given windmill may be reduced by 10 to 15% depending on the relevant wind speed.
Thus, it has been realized that it is desirable to carry out a cleaning and subsequent sealing of the windmill wings on a regular basis, depending on the relevant location of the windmill.
So far, such cleanings have been carried out manually by bringing the windmill to a stop and locking it into positions in which the rotor blades point towards the ground. Subsequently, each rotor blade has been rinsed individually and manually by using various arrangements to provide the manpower with the necessary work position and height.
Such a hoisting arrangement is known from German utility model DE 296 03 278 U in which suspension means are fastened to each of the two rotor blades near the hub of the rotor once the windmill has been brought to a stop and with one rotor blade pointing straight downwards. A special work platform with a through-going slit at the bottom has been fixed to these suspension means so that the rotor blade pointing downwards could be inserted into this slit. The work platform has subsequently been hoisted upwards in a stepwise manner, while the crew has rinsed the surface of the rotor blade manually, e.g. with one person located on each side of the rotor blade.
Even with such an arrangement, it is a time-consuming process to carry out a cleaning of the rotor blades of a windmill, just as such a known arrangement would probably require the use of machinery, such as a crane, for fixation of the suspension means. Thus, it could be claimed that two individuals, when mid-sized windmills are involved, would probably not be able to clean more than 4 windmills per day.